Can I Record
The Police?
In Canada, you have a general right to record police officers in the execution of their duties in a public place. Canada is a One-Party Consent country.
The "One-Party" Rule
You can record any conversation that you are a part of. You do not need the other person's permission.
Visual recording in public is a Charter right.
Audio recording of your own interaction is 100% legal.
Do not obstruct or interfere. Stay at a safe distance.
The Legal Foundation
The Criminal Code of Canada (Section 184) prohibits the interception of private communications. However, there is a major exception: it is not a crime if one of the parties to the conversation consents to the recording.
Because you are a party to the interaction with the police, your own consent is sufficient to make the recording legal.
The "Public Duty" Exception
Courts in Canada have consistently found that police officers performing their duties in public do not have a "reasonable expectation of privacy." Therefore, even if you are recording a conversation between other people (as a bystander), it may still be legal if the setting is public enough that the conversation could be overheard.
What if they take my phone?
Police cannot demand that you delete a video. They cannot delete it themselves. To seize the phone as evidence, they generally need a warrant or to prove that the evidence might be destroyed if they don't act immediately (Exigent Circumstances).